Huntington's Disease is an autosomal dominant neurologic disorder characterized by chorea, eye movement abnormalities, and dementia. Significant weight loss is a common finding early in the course of the disease despite reportedly normal or increased caloric intakes. The cause of this apparent increase in energy expenditure is not known. We hypothesize that energy expenditure is increased in patients with Huntigton's Disease as a consequence of the movement disorder. To test this, basal metabolic rate, 24-hour energy expenditure, and non-resting energy expenditure (all measured using the human respiratory chamber on the Research Ward of the Clinical Diabetes and Nutrition Section), and 7-day free-living energy expenditure (measured using the doubly-labeled water technique) will be compared in three groups of patients with Huntington's Disease with varying degrees of chorea (asymptomatic, mild, and moderate) and age, sex, and weight matched controls. To correct energy expenditure for differences in metabolically active (primarily lean) body mass among subjects, all individuals will have body composition measured by anthropometry, bioelectrical impedance analysis, and dual energy X-ray absorptiometry scanning. In addition, since the reported prevalence of non-insulin dependent diabetes is 7 times higher in patients with Huntington's Disease than in the general population, all patients will also undergo an oral glucose tolerance test with measurement of plasma insulin levels. Comparison of asymptomatic patients with Huntington's Disease and controls will address whether an inherent abnormality in energy metabolism is present in Huntington's Disease, whereas comparison of patients with varying degrees of chorea will address the contribution of the movement disorder to the apparent increase in energy expenditure. In addition to providing insight into the pathophysiologic abnormalities in Huntington's Disease, this study may also improve the care of patients with Huntington's Disease by providing more precise estimates of their caloric needs.